This is the first competitive renewal of an RO1 that proposes to characterize the function of a newly isolated gene that is mutated in fidget mice, and which the PI has named fidgetin. In the previous funding cycle, the PI identified the gene by positional cloning as a novel member of a divergent class of proteins, the AAA group, that share an ATPase domain, and which may function generally in processes of protein folding and unfolding. Although the gene is widely expressed, it's loss of function gives rise to a set of remarkably specific developmental phenotypes whose molecular and cellular underpinnings are obscure. The current application will investigate these underpinnings by determining the subcellular location of fidgetin with a lacZ fusion protein generated by gene targeting, epitope-tagged constructs introduced into culture cells, and generating antisera to localize the endogenous protein by immunocytochemistry (Aim 1). Fidgetin-interacting proteins will be identified in Aim 2 using a yeast two-hybrid screen followed by in vivo expression and co-immunoprecipitation studies. In Aim 3, careful analyses of fidgetin RNA expression during embryonic development of normal and various mutant mice will be carried out in the context of hypotheses that fidgetin is either upstream or downstream of genes previously shown when mutated to cause defects similar to fidget. Finally, Aim 4 will attempt to gain insight into possible redundancy and action of fidget-related genes by expression studies, modifier gene mapping, and gene targeting.